The present embodiments relate to a method for reducing mechanical vibrations in a magnetic resonance imaging system, a gradient system for reducing mechanical vibrations, and a magnetic resonance imaging system with a gradient system for reducing mechanical vibrations.
Imaging systems that utilize magnetic resonance measurement (e.g., nuclear resonance or magnetic resonance tomographs) have been established and proven through numerous applications. In these systems, a static basic magnetic field may be used for data acquisition. The static basic magnetic field, which is used for initial alignment and homogenization of magnetic dipoles to be examined, is overlaid for local resolution of the imaging signal with a rapidly switched magnetic field (e.g., the gradient field). Depending on the mode of operation of the imaging system, different switching sequences and magnetic field strengths are applied. The gradient coil system or gradient system for generating the gradient field may be a rapidly switched electrically-operated magnet system with one or more gradient coils, which may generate magnetic fields in spatial directions x, y and z orthogonal to one another. The gradient coils are molded into a gradient body.
Because of the interaction of the gradient system with the basic magnetic field, which may have high magnetic field strengths of a few Tesla, the gradient system is subjected to immense stress forces. In such cases, the gradient system, depending on the operating state of the imaging system, may be excited into strong mechanical vibrations. The mechanical vibrations depend on, inter alia, factors such as the frequency of the switchover of the gradient field from the damping by the support of the gradient field. The general system conditions of support and damping as well as the mechanical properties of the gradient system result in the formation of natural vibrations of the gradient system in the magnetic resonance imaging system.
To improve the image quality (e.g., improve the signal-to-noise ratio), the basic magnetic fields mostly generated with the aid of superconducting magnetic coils reach strengths of 3 Tesla and more. In operation, however, as the operating current of the superconducting coils is increased, the danger that the superconductivity of the superconducting magnetic coils will be lost or decrease increases.
Stray fields of the gradient system lead to high loads on the basic magnet system and, for example, induce eddy currents in a cold shield of the superconducting basic magnetic system, which may include conductive materials. The induction of eddy currents may lead to an increased heat input into the cooling system of basic magnets and may, in some cases, even lead to the collapse of the superconductivity during the normal operation of the magnetic resonance imaging system. The magnetic resonance imaging system may be permanently destroyed by this.
In addition, the Lorentz forces acting on the gradient system strengthen as the strength of the basic magnetic field increases, so that the vibration excitation of a gradient system in a basic magnetic field of the described strength leads to greater noise loading and may also adversely affect the image capture.
Thus, the interaction of stray fields of the gradient system is suppressed (e.g., in relation to the basic magnet that generates the basic magnetic field of 3 or more T. In addition, mechanical vibrations may be reduced, or the excitation of the mechanical vibrations may be weakened.